The whole thing was arranged by Capone’s underling Jack “Machine Gun” McGurn (not to be confused with George “Machine Gun” Kelley) who was actually trying to put the hit on Moran himself. McGurn got a bootlegger associate of his to arrange a sale of whiskey to Moran's gang at a parking garage on Chicago's North Side. While the booze deal was being made, four of McGurn's assassins, who were dressed as policemen, drove up in a stolen police car and pretended they were conducting a raid. They lined Moran's men up against a wall and opened fire. Moran, who was supposed to be there, showed up late. And when he saw the police car outside of the garage, he fled.
It didn't take much for other gangs, the police, and newspaper reporters to figure out that Al Capone had ordered the hit. There was no evidence that would have stood up in court, but the war between Capone and McGurn was well known. The press ended up having a field day with the event they called the "St. Valentine's Day Massacre."
The St. Valentine's Day Massacre (Crimelibrary.com)
FBI files: St. Valentine's Day Massacre, Al Capone, and Bugs Moran.
